JP2017103480A - Semiconductor device manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide stable electrical characteristics to a semiconductor device using an oxide semiconductor to improve reliability.SOLUTION: In a transistor including an oxide semiconductor film, by forming an insulation film next to the oxide semiconductor film with use of a material containing a group 13 element and oxygen, a good state of an interface with the oxide semiconductor film is maintained. When the insulation film includes a region containing oxygen more than a stoichiometric composition ratio, oxygen is supplied to the oxide semiconductor film and oxygen defects in the oxide semiconductor film are reduced. And when the insulation film next to the oxide semiconductor film has a layered structure and an aluminum-containing film is provided above and below the oxide semiconductor film, water intrusion into the oxide semiconductor film is prevented.SELECTED DRAWING: Figure 1

Description

The present invention relates to a semiconductor device and a manufacturing method thereof.

Note that in this specification, a semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.

A technique for forming a transistor using a semiconductor thin film formed over a substrate having an insulating surface has attracted attention. The transistor is widely applied to electronic devices such as an integrated circuit (IC) and an image display device (display device). A silicon-based semiconductor material is widely known as a semiconductor thin film applicable to a transistor, but an oxide semiconductor has attracted attention as another material.

For example, a transistor using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) having an electron carrier concentration of less than 10 ¹⁸ / cm ³ as an active layer of the transistor is disclosed. (See Patent Document 1).

JP 2006-165528 A

However, the electrical conductivity of an oxide semiconductor may change if it deviates from the stoichiometric composition due to oxygen deficiency or the like, or if hydrogen or water that forms an electron donor is mixed in the device manufacturing process. There is. Such a phenomenon becomes a factor of variation in electrical characteristics for a semiconductor device such as a transistor including an oxide semiconductor.

In view of such a problem, an object is to provide a semiconductor device including an oxide semiconductor with stable electrical characteristics and improve reliability.

In one embodiment of the disclosed invention, an insulating film in contact with the oxide semiconductor film is formed using a material containing a Group 13 element and oxygen, whereby the state of the interface with the oxide semiconductor film can be kept favorable. . Further, the insulating film includes a region where oxygen is higher than the stoichiometric composition ratio,
Oxygen can be supplied to the oxide semiconductor film, so that oxygen defects in the oxide semiconductor film can be reduced.
In addition, when the insulating film in contact with the oxide semiconductor film has a stacked structure and the films containing aluminum are provided above and below the oxide semiconductor film, entry of water into the oxide semiconductor film can be prevented. More specifically, for example, the following configuration can be adopted.

One embodiment of the present invention is in contact with a gate electrode, a gate insulating film that covers the gate electrode and includes a stacked structure of a first metal oxide film and a second metal oxide film, and the second metal oxide film. An oxide semiconductor film provided in a region overlapping with the gate electrode, a source electrode and a drain electrode electrically connected to the oxide semiconductor film, a third metal oxide film in contact with the oxide semiconductor film, A fourth metal oxide film in contact with the third metal oxide film, and each of the first to fourth metal oxide films includes a group 13 element and oxygen.

In the above semiconductor device, a conductive layer may be provided over the fourth metal oxide film and in a region overlapping with the oxide semiconductor film.

Another embodiment of the present invention is a first metal oxide film, a second metal oxide film provided in contact with the first metal oxide film, and a second metal oxide film. An oxide semiconductor film in contact with the oxide semiconductor film; a source electrode and a drain electrode electrically connected to the oxide semiconductor film; a third metal oxide film in contact with the oxide semiconductor film; and a third metal oxide film in contact with the oxide semiconductor film. A gate insulating film including a stacked structure of a fourth metal oxide film provided on the gate insulating film, and a gate electrode provided on the gate insulating film and in a region overlapping with the oxide semiconductor film, Each of the first to fourth metal oxide films is a semiconductor device containing a Group 13 element and oxygen.

In any one of the above semiconductor devices, it is preferable that at least a part of the second metal oxide film and the third metal oxide film are provided in contact with each other.

In any one of the above semiconductor devices, each of the first to fourth metal oxide films preferably includes a region where oxygen is higher than the stoichiometric composition ratio.

In any one of the semiconductor devices described above, it is preferable that the first metal oxide film and the fourth metal oxide film each contain either or both of aluminum oxide and aluminum gallium oxide.

In any one of the semiconductor devices described above, it is preferable that the second metal oxide film and the third metal oxide film each contain either or both of gallium oxide and gallium aluminum oxide.

The ordinal numbers attached as the first and second are used for convenience and do not indicate the order of steps or the order of lamination. In addition, a specific name is not shown as a matter for specifying the invention in this specification.

According to one embodiment of the present invention, a transistor having stable electrical characteristics is provided.

Alternatively, according to one embodiment of the present invention, a semiconductor device including a transistor with favorable electric characteristics and high reliability is provided.

2A and 2B are a plan view and a cross-sectional view illustrating one embodiment of a semiconductor device. 2A and 2B are a plan view and a cross-sectional view illustrating one embodiment of a semiconductor device. 2A and 2B are a plan view and a cross-sectional view illustrating one embodiment of a semiconductor device. FIG. 14 is a cross-sectional view illustrating one embodiment of a semiconductor device. 10A and 10B illustrate an example of a manufacturing process of a semiconductor device. 10A and 10B illustrate an example of a manufacturing process of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. FIG. 9 illustrates an electronic device. 2A and 2B are a plan view and a cross-sectional view illustrating one embodiment of a semiconductor device. 2A and 2B are a plan view and a cross-sectional view illustrating one embodiment of a semiconductor device. 2A and 2B are a plan view and a cross-sectional view illustrating one embodiment of a semiconductor device. 2A and 2B are a plan view and a cross-sectional view illustrating one embodiment of a semiconductor device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that the modes and details can be variously changed. In addition, the present invention is not construed as being limited to the description of the embodiments below.

(Embodiment 1)
In this embodiment, one embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS.

<Configuration example of semiconductor device>
FIG. 1 is a plan view and a cross-sectional view of a transistor 310 as an example of a semiconductor device according to one embodiment of the disclosed invention. In FIG. 1, a bottom-gate transistor is illustrated as a transistor according to one embodiment of the disclosed invention. Here, FIG. 1A is a plan view, and FIG.
FIGS. 1B and 1C are cross-sectional views taken along lines AB and CD, respectively, in FIG. Note that in FIG. 1A, some components of the transistor 310 (e.g., the third metal oxide film 407 and the fourth metal oxide film 4 are omitted in order to avoid complexity).
09 etc.) is omitted.

A transistor 310 illustrated in FIG. 1 includes a gate electrode 401 over a substrate 400 having an insulating surface.
A gate insulating film composed of a first metal oxide film 402 and a second metal oxide film 404;
The oxide semiconductor film 403 includes a source electrode 405a, a drain electrode 405b, a third metal oxide film 407, and a fourth metal oxide film 409.

In the transistor 310 illustrated in FIG. 1, the third metal oxide film 407 includes the source electrode 40.
5a and the drain electrode 405b, and in contact with the second metal oxide film 404 and the oxide semiconductor film 403. In the transistor 310 illustrated in FIG.
The third metal oxide film 407 and the second metal oxide film 404 are in contact with each other in a region where the oxide semiconductor film 403 does not exist. That is, the oxide semiconductor film 403 is provided so as to be surrounded by the second metal oxide film 404 and the third metal oxide film 407.

Here, when the oxide semiconductor film 403 is sufficiently removed of impurities such as hydrogen and water,
Alternatively, it is desirable that the material be purified by supplying sufficient oxygen. Specifically, for example, the hydrogen concentration of the oxide semiconductor film 403 is 5 × 10 ¹⁹ atoms / c.
m ³ or less, preferably 5 × 10 ¹⁸ atoms / cm ³ or less, more preferably 5 × 10 ^1
7 atoms / cm ³ or less. Note that the hydrogen concentration in the oxide semiconductor film 403 is as follows.
Secondary ion mass spectrometry (SIMS: Secondary Ion Mass Spec
lossy). As described above, in the oxide semiconductor film 403 in which the hydrogen concentration is sufficiently reduced to be highly purified, and the defect level in the energy gap due to oxygen deficiency is reduced by supplying sufficient oxygen, the carrier concentration is 1 × less than 10 ¹² / cm ³ ,
Desirably, it is less than 1 × 10 ¹¹ / cm ³ , more desirably less than 1.45 × 10 ¹⁰ / cm ³ . In this manner, a transistor having favorable electric characteristics can be obtained by using an i-type oxide semiconductor.

As the second metal oxide film 404 or the third metal oxide film 407 in contact with the oxide semiconductor film 403, an insulating film containing oxygen is preferably used, and a region containing more oxygen than the stoichiometric composition ratio ( A film including an oxygen-excess region is more preferable. Oxide semiconductor film 403
The second metal oxide film 404 and the third metal oxide film 407 which are in contact with each other have an oxygen-excess region, so that the second metal oxide film 404 or the third metal oxide film can be formed from the oxide semiconductor film 403. The movement of oxygen to 407 can be prevented. In addition, oxygen can be supplied from the second metal oxide film 404 or the third metal oxide film 407 to the oxide semiconductor film 403. Therefore, the oxide semiconductor film 403 sandwiched between the second metal oxide film 404 and the third metal oxide film 407 can be a film containing a sufficient amount of oxygen.

Note that many oxide semiconductor materials used for the oxide semiconductor film 403 include a Group 13 element. Therefore, the oxide semiconductor film 40 is formed using a material containing a Group 13 element and oxygen.
By forming the second metal oxide film 404 or the third metal oxide film 407 in contact with the oxide semiconductor film 3, the state of the interface with the oxide semiconductor film can be kept favorable. This is because a material containing a Group 13 element and oxygen is compatible with an oxide semiconductor material.

For example, in the case of forming an oxide semiconductor film containing gallium, a material containing gallium oxide is used for the second metal oxide film 404 or the third metal oxide film 407 so that the oxide semiconductor film The interface characteristics with the metal oxide film in contact with the oxide semiconductor film can be kept good. By providing the oxide semiconductor film and the metal oxide film containing gallium oxide in contact with each other, hydrogen pileup at the interface between the oxide semiconductor film and the metal oxide film can be reduced. Note that a similar effect can be obtained when an element belonging to the same group as the constituent element of the oxide semiconductor is used. That is, it is also effective to form the second metal oxide film 404 or the third metal oxide film 407 using a material containing aluminum oxide or the like. Note that aluminum oxide has a characteristic that water does not easily permeate, and thus the use of the material is preferable in terms of preventing water from entering the oxide semiconductor film.

Two or more Group 13 elements included in the second metal oxide film 404 or the third metal oxide film 407 may be used. For example, the above-described material such as gallium aluminum oxide (or aluminum gallium oxide) containing gallium and aluminum may be used for the second metal oxide film 404 or the third metal oxide film 407. In this case, since the effect resulting from containing gallium and the effect resulting from containing aluminum can be obtained together, it is preferable. For example, by providing an oxide semiconductor film and a metal oxide film containing gallium and aluminum in contact with each other, water can be prevented from entering the oxide semiconductor film, and the interface between the oxide semiconductor film and the metal oxide film can be prevented. The pile-up of hydrogen (including hydrogen ions) in can be sufficiently reduced.

Here, aluminum gallium oxide indicates that the aluminum content (atomic%) is higher than gallium content (atomic%), and gallium aluminum oxide means that the gallium aluminum content is higher than the aluminum content (atomic%). Indicates a large amount (atomic%).

Note that aluminum has a lower electronegativity than gallium, and thus aluminum may adsorb hydrogen more easily than gallium. Therefore, in order to suppress hydrogen pileup at the interface with the oxide semiconductor film, the metal oxide film in contact with the oxide semiconductor film is a gallium oxide film or a gallium oxide film having a high gallium content. It is more preferable to use an aluminum film.

Further, the second metal oxide film 404 and the third metal oxide film 407 are formed using the same material, whereby the second metal oxide film 4 is formed in a region where the oxide semiconductor film 403 does not exist.
04 and the third metal oxide film 407 are preferably in contact with each other because adhesion can be improved. In addition, it is more preferable that the ratio of the constituent elements of the second metal oxide film 404 is equal to the ratio of the constituent elements of the third metal oxide film 407. For example, when a gallium oxide film or a gallium aluminum oxide film is used as the second or third metal oxide film, Ga _x Al _2−x O _{3 + α} (1 <x ≦ 2, 0 <α <1) is satisfied. Is preferred.

In the transistor 310, the first metal oxide film 402 is the second metal oxide film 404.
And function as a gate insulating film. In the transistor 310, the fourth metal oxide film 409 is a film which is stacked with the third metal oxide film 407 and functions as a protective film. The first metal oxide film 402 and the fourth metal oxide film 409 are formed in the thirteenth
It is preferable to use a material containing a group element and oxygen because the state of the interface with the second metal oxide film 404 or the third metal oxide film 407 can be kept favorable. Note that as described above, aluminum oxide has a characteristic that water is difficult to permeate. Therefore, as the first or fourth metal oxide film covering the upper and lower portions of the transistor 310, an oxide containing a large amount of aluminum is used. The application of the aluminum gallium film is preferable in terms of preventing water from entering the oxide semiconductor film.

In addition, the first metal oxide film 402 and the fourth metal oxide film 409 preferably include a region where oxygen is higher than the stoichiometric composition ratio. Accordingly, oxygen is supplied to the metal oxide film or the oxide semiconductor film 403 in contact with the oxide semiconductor film 403, and the oxide semiconductor film 403 or at the interface between the oxide semiconductor film 403 and the metal oxide film in contact with the oxide semiconductor film 403 is supplied. Oxygen defects can be reduced. For example, when an aluminum gallium oxide film is used as the first or fourth metal oxide film, Ga _x Al _2−x O _{3 + α} (0 <x <1, 0 <α <1) is preferable.

Note that in the case where an oxide semiconductor film having no defects (oxygen defects) is used, the first to fourth metal oxide films and the like may contain oxygen in an amount corresponding to the stoichiometric composition. However, in order to ensure reliability, such as suppressing fluctuations in the threshold voltage of the transistor, the metal oxide film has a chemical structure in consideration of the fact that an oxygen deficient state may occur in the oxide semiconductor film. It is preferable to contain oxygen more than the stoichiometric composition ratio.

Further, an insulator may be provided over the transistor 310. A source electrode 405a and a drain electrode 405b which are electrically connected to the oxide semiconductor film 403;
In order to electrically connect the wiring, openings may be formed in the first to fourth metal oxide films or the like. Note that although the oxide semiconductor film 403 is preferably processed into an island shape, the oxide semiconductor film 403 may not be processed into an island shape.

2A and 2B are a cross-sectional view and a plan view of a transistor 320 having a structure different from that of the transistor 310. FIG. In FIG. 2, a top-gate transistor is illustrated as a transistor according to one embodiment of the disclosed invention. FIG. 2A is a plan view, and FIGS. 2B and 2C are cross-sectional views taken along lines EF and GH in FIG. Note that FIG.
), Some of the components of the transistor 320 (e.g.,
The third metal oxide film 407 and the fourth metal oxide film 409 are omitted.

2 includes a first metal oxide film 402, a second metal oxide film 404, an oxide semiconductor film 403, and a source electrode 405 over a substrate 400 having an insulating surface.
a, the drain electrode 405b, the third metal oxide film 407 and the fourth metal oxide film 4
09 and a gate electrode 414.

In the transistor 320 illustrated in FIG. 2, the third metal oxide film 407 includes the source electrode 40.
5a and the drain electrode 405b, and in contact with part of the second metal oxide film 404 and the oxide semiconductor film 403. Similarly to the transistor 310 illustrated in FIG. 1, in the transistor 320 illustrated in FIG. 2, the third metal oxide film 407 and the second metal oxide film 404 are regions where the oxide semiconductor film 403 does not exist. Is touching. That is, the oxide semiconductor film 403 includes the second metal oxide film 404 and the third metal oxide film 407.
Surrounded by and. For other components, the transistor 310 in FIG.
It is the same. For details, the description regarding FIG. 1 can be referred to.

In FIG. 3, the transistor 3 having a different configuration from the transistors 310 and 320
30 is a cross-sectional view and a plan view. Here, FIG. 3A is a plan view, and FIG. 3B and FIG. 3C are cross-sectional views of the IJ cross section and the KL cross section in FIG. 3A, respectively. is there. Note that in FIG. 3A, some components of the transistor 330 (eg, the third metal oxide film 407 and the fourth metal oxide film 409) are omitted to avoid complexity. ing.

3 includes a gate electrode 401 over a substrate 400 having an insulating surface.
A gate insulating film composed of a first metal oxide film 402 and a second metal oxide film 404;
The oxide semiconductor film 403, the source electrode 405 a, the drain electrode 405 b, the third metal oxide film 407, the fourth metal oxide film 409, and the oxide semiconductor film 403 are provided in overlapping regions. And a conductive layer 410.

In the transistor 330 illustrated in FIG. 3, the third metal oxide film 407 includes the source electrode 40.
5a and the drain electrode 405b, and in contact with the second metal oxide film 404 and the oxide semiconductor film 403. Similarly to the transistor 310 illustrated in FIG.
In the transistor 330 illustrated in FIG. 3, the third metal oxide film 407 and the second metal oxide film 404 are in contact with each other in a region where the oxide semiconductor film 403 does not exist. That means
The oxide semiconductor film 403 is provided so as to be surrounded by the second metal oxide film 404 and the third metal oxide film 407.

In the transistor 330, the conductive layer 410 can function as a second gate electrode. In that case, the third metal oxide film 407 and the fourth metal oxide film 409 function as gate insulating films. Other components are similar to those of the transistor 310 in FIG. For details, the description regarding FIG. 1 can be referred to.

4A to 4F are cross-sectional views of transistors having different structures from the above transistors. Note that the configuration in FIG. 4 can be combined with the configurations in FIGS. 1 to 3 as appropriate.

A transistor 340 illustrated in FIG. 4A includes a gate electrode 401, a gate insulating film including a first metal oxide film 402 and a second metal oxide film 404, an oxide film over a substrate 400 having an insulating surface. A physical semiconductor film 403, a source electrode 405a, a drain electrode 405b, and a third
Transistor 31 in that the metal oxide film 407 and the fourth metal oxide film 409 are included.
Common to 0. A difference between the transistor 340 and the transistor 310 is a position where the oxide semiconductor film 403 is connected to the source electrode 405a and the drain electrode 405b. That is, in the transistor 340, the oxide semiconductor film 4 is formed below the oxide semiconductor film 403.
03 is in contact with the source electrode 405a and the drain electrode 405b. Other components are similar to those of the transistor 310 in FIG. For details, the description regarding FIG. 1 can be referred to.

A transistor 350 illustrated in FIG. 4B includes a first metal oxide film 402, a second metal oxide film 404, an oxide semiconductor film 403, and a source electrode 405a over a substrate 400 having an insulating surface. Transistor 32 in that it includes a drain electrode 405b, a gate insulating film made of the third metal oxide film 407 and the fourth metal oxide film 409, and a gate electrode 414.
Common to 0. A difference between the transistor 350 and the transistor 320 is a position where the oxide semiconductor film 403 is connected to the source electrode 405a and the drain electrode 405b. That is, in the transistor 350, the oxide semiconductor film 4 is formed below the oxide semiconductor film 403.
03 is in contact with the source electrode 405a and the drain electrode 405b. Other components are similar to those of the transistor 320 in FIG. For details, the description regarding FIG. 2 can be referred to.

A transistor 360 illustrated in FIG. 4C includes a gate electrode 401, a gate insulating film including a first metal oxide film 402 and a second metal oxide film 404, and an oxide film over a substrate 400 having an insulating surface. A physical semiconductor film 403, a source electrode 405a, a drain electrode 405b, and a third
The transistor 330 is common to the transistor 330 in that it includes the metal oxide film 407, the fourth metal oxide film 409, and the conductive layer 410 provided in a region overlapping with the oxide semiconductor film 403.
A difference between the transistor 360 and the transistor 330 is a position where the oxide semiconductor film 403 is connected to the source electrode 405a and the drain electrode 405b. That is, transistor 3
In 60, the oxide semiconductor film 403 is in contact with the source electrode 405a and the drain electrode 405b under the oxide semiconductor film 403. Other components are the same as those of the transistor 330 in FIG. For details, the description regarding FIG. 3 can be referred to.

A transistor 370 illustrated in FIG. 4D includes a gate electrode 401, a gate insulating film including a first metal oxide film 402 and a second metal oxide film 404, and an oxide film over a substrate 400 having an insulating surface. A physical semiconductor film 403, a source electrode 405a, a drain electrode 405b, and a third
Transistor 31 in that the metal oxide film 407 and the fourth metal oxide film 409 are included.
Common to 0. The difference between the transistor 370 and the transistor 310 is that in the transistor 370, the third metal oxide film 407 and the second metal oxide film 404, and the first metal oxide film 402 and the fourth metal oxide film are used. 409 is an oxide semiconductor film 403
It is a point touching in a region where no. In the transistor 370, in addition to the second metal oxide film 404 and the third metal oxide film 407, the first metal oxide film 40
Since the oxide semiconductor film 403 is also surrounded by the second and fourth metal oxide films 409, impurities such as hydrogen or moisture can be further prevented. 4D (D
The structure of the transistor 370 shown in FIG. 6 can be formed by patterning the third metal oxide film 407 and the second metal oxide film 404 after the third metal oxide film 407 is formed, for example. it can. For the first metal oxide film 402 and the second metal oxide film 404, it is preferable to select materials that can achieve an etching selectivity. Other components are similar to those of the transistor 310 in FIG. For details, the description regarding FIG. 1 can be referred to.

Note that two metal oxide films are not necessarily provided above and below the oxide semiconductor film 403. For example, in the transistor 380 illustrated in FIG. 4E, the stacked structure of the third metal oxide film 407 and the fourth metal oxide film 409 in the transistor 310 is a single-layer structure of the metal oxide film 413. In the transistor 390 illustrated in FIG. 4F, the stacked structure of the first metal oxide film 402 and the second metal oxide film 404 in the transistor 310 is a single-layer structure of the metal oxide film 411. It is an example. The metal oxide film 413 or the metal oxide film 411 can be formed using a material containing a Group 13 element and oxygen. For example, any of gallium oxide, aluminum oxide, aluminum gallium oxide, and gallium aluminum oxide can be used. A material including one or more can be used. Also,
The metal oxide film 413 or the metal oxide film 411 preferably has an oxygen-excess region similarly to the first to fourth metal oxide films described above. Other components are similar to those of the transistor 310 in FIG. For details, the description regarding FIG. 1 can be referred to.

<Example of transistor manufacturing process>
Hereinafter, an example of a manufacturing process of the transistor according to this embodiment will be described with reference to FIGS.

<Manufacturing Process of Transistor 330>
An example of a manufacturing process of the transistor 330 illustrated in FIGS. 3A to 3C will be described with reference to FIGS. Note that the transistor 310 illustrated in FIG. 1 has a structure in which the conductive layer 410 is omitted from the structure of the transistor 330 and the transistor 33 is provided except that the conductive layer 410 is provided.
It can be manufactured in the same manner as the manufacturing process of 0.

First, after a conductive film is formed over the substrate 400 having an insulating surface, the gate electrode 401 is formed by a first photolithography process. Note that the resist mask may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

There is no particular limitation on a substrate that can be used as the substrate 400 having an insulating surface as long as it has heat resistance enough to withstand heat treatment performed later. For example, a substrate such as a glass substrate, a ceramic substrate, a quartz substrate, or a sapphire substrate can be used. In addition, a single crystal semiconductor substrate such as silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate such as silicon germanium, an SOI substrate, or the like can be used as long as it has an insulating surface. A semiconductor element may be provided thereover. Further, a flexible substrate may be used as the substrate 400.

An insulating film serving as a base film may be provided between the substrate 400 and the gate electrode 401. Undercoat film
It has a function of preventing diffusion of an impurity element from the substrate 400 and may be formed using a stacked structure including one or more films selected from a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, and a silicon oxynitride film. it can.

In addition, the gate electrode 401 may be formed as a single layer or a stacked layer using a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material containing these as a main component. it can.

Next, a first metal oxide film 402 is formed over the gate electrode 401. The first metal oxide film 402 can be formed using a material including a Group 13 element and oxygen.
A material containing one or more of gallium oxide, aluminum oxide, aluminum gallium oxide, and gallium aluminum oxide can be used. Note that in order to maintain a favorable state of the interface with the second metal oxide film 404 to be formed later and to prevent water from entering the oxide semiconductor film, the first metal oxide film 402 is used. It is more preferable to apply an aluminum gallium oxide film.

Alternatively, the first metal oxide film 402 may include a third group such as yttrium in addition to the group 13 element.
Group elements, Group 4 elements such as hafnium, Group 14 elements such as silicon, or impurity elements other than hydrogen such as nitrogen can be included. By including such an impurity element, for example, exceeding about 0 and about 20 atomic% or less, the energy gap of the first metal oxide film 402 can be controlled by the addition amount of the element.

The first metal oxide film 402 is preferably formed by a method in which impurities such as hydrogen and water are not mixed. When an impurity such as hydrogen or water is contained in the first metal oxide film 402, an oxide semiconductor film caused by an intrusion of impurities such as hydrogen or water into an oxide semiconductor film to be formed later or an impurity such as hydrogen or water This is because the resistance of the oxide semiconductor film is reduced (n-type) due to extraction of oxygen therein, and a parasitic channel may be formed. The first metal oxide film 402 is preferably formed by, for example, a sputtering method. As a sputtering gas used for film formation, a high-purity gas from which impurities such as hydrogen and water are removed is preferably used.

As the sputtering method, a DC sputtering method using a DC power source, a pulse DC sputtering method in which a DC bias is applied in a pulsed manner, an AC sputtering method, or the like can be used.

Note that when an aluminum gallium oxide film or a gallium aluminum oxide film is formed as the first metal oxide film 402, a gallium oxide target to which aluminum particles are added may be used as a target used in a sputtering method. . By using a gallium oxide target to which aluminum particles are added, the conductivity of the target can be increased, so that discharge during sputtering can be facilitated. By using such a target, a metal oxide film suitable for mass production can be manufactured.

Next, treatment for supplying oxygen to the first metal oxide film 402 is desirably performed. Examples of the treatment for supplying oxygen include heat treatment in an oxygen atmosphere, oxygen doping treatment, and the like. Or
Oxygen may be added by irradiation with oxygen ions accelerated by an electric field. Note that in this specification and the like, oxygen doping treatment means adding oxygen to the bulk, and the term bulk is used to clarify that oxygen is added not only to the surface of the thin film but also to the inside of the thin film. ing. Also,
The oxygen dope includes oxygen plasma dope in which plasma oxygen is added to the bulk.

By performing a process of supplying oxygen such as an oxygen doping process on the first metal oxide film 402, a region containing more oxygen than the stoichiometric composition ratio is formed in the first metal oxide film 402. Is done. By providing such a region, oxygen can be supplied to the second metal oxide film or the oxide semiconductor film to be formed later, and oxygen defects in the oxide semiconductor film or at the interface can be reduced.

Alternatively, when the first metal oxide film 402 is formed by a sputtering method, an oxygen gas or an inert gas (for example, a rare gas such as argon or nitrogen) and a mixed gas of oxygen are introduced. Thus, an oxygen-excess region can be formed in the first metal oxide film 402. Note that heat treatment may be performed after the film formation by a sputtering method.

For example, in the case where an aluminum gallium oxide film is used as the first metal oxide film 402, Ga _x Al _2−x O _{3 + α} (0
<X <1, 0 <α <1).

Next, a second metal oxide film 404 is formed over the first metal oxide film 402 (FIG. 5A).
)). As a result, a gate insulating film (first gate insulating film) made of the first metal oxide film 402 and the second metal oxide film 404 is formed. The second metal oxide film 404 is the first
For example, a material containing any one or more of gallium oxide, aluminum oxide, aluminum gallium oxide, and gallium aluminum oxide can be used. Note that, as described above, in order to maintain a favorable state of the interface with the oxide semiconductor film to be formed later and to suppress hydrogen pileup at the interface with the oxide semiconductor film, the second metal oxide is used. It is more preferable to use a gallium aluminum oxide film as the material film 404.

Similar to the first metal oxide film 402, the second metal oxide film 404 includes a Group 3 element such as yttrium, a Group 4 element such as hafnium, silicon, in addition to the Group 13 element. Or an impurity element other than hydrogen, such as nitrogen, may be included.

The second metal oxide film 404 is preferably formed by a method in which impurities such as hydrogen and water are not mixed, for example, a sputtering method can be applied. Details are first
The formation method of the first metal oxide film 402 can be referred to in the same manner as the metal oxide film 402 in FIG.

Next, treatment for supplying oxygen to the second metal oxide film 404 is desirably performed. Examples of the treatment for supplying oxygen include heat treatment in an oxygen atmosphere, oxygen doping treatment, and the like. Or
Oxygen may be added by irradiation with oxygen ions accelerated by an electric field.

Alternatively, when the second metal oxide film 404 is formed by a sputtering method, an oxygen gas or a mixed gas of an inert gas (for example, a rare gas such as argon or nitrogen) and oxygen is introduced. As a result, oxygen may be supplied to the second metal oxide film 404. For example, when forming a gallium oxide film, the distance between the substrate and the target is 60 mm, and the pressure is 0.4 P.
a, the RF power source is 1 kW, the film forming temperature is room temperature, and the flow rate of argon gas is 25 scc.
m, and the flow rate of oxygen gas can be 25 sccm. The film forming temperature is not limited to room temperature, and may be 400 ° C., for example. Further, the flow rate of oxygen gas may be 50 sccm without introducing argon gas. Alternatively, heat treatment (for example, 450 ° C. to 650 ° C. for 1 hour in ultra-dry air) may be performed after film formation by a sputtering method. By these film formation methods, a gallium oxide film containing more oxygen than the stoichiometric composition ratio can be formed, and Ga ₂ O _{3 + α} (0 <α <1, for example, 0.32 ≦ α ≦ 0.48). ).

By performing treatment for supplying oxygen such as oxygen doping treatment (hereinafter also referred to as oxygen supply treatment) to the second metal oxide film 404, the second metal oxide film 404 has a stoichiometric amount. A region having more oxygen than the target composition ratio is formed. With such a region, oxygen can be supplied to an oxide semiconductor film to be formed later, and oxygen defects in the oxide semiconductor film or at an interface can be reduced. Note that the oxygen supply treatment to the second metal oxide film 404 is performed in accordance with the first process described above.
The oxygen supply treatment to the metal oxide film 402 may also be performed.

In the case where a gallium oxide film or a gallium aluminum oxide film is used as the second metal oxide film 404, Ga _x Al _2−x O _{3+ is} obtained by performing oxygen supply treatment such as oxygen doping treatment.
_α (1 <x ≦ 2, 0 <α <1) is preferable.

Next, an oxide semiconductor film 403 with a thickness of 3 nm to 30 nm is formed over the second metal oxide film 404 by a sputtering method. When the thickness of the oxide semiconductor film 403 is excessively large (for example, when the thickness is 50 nm or more), the transistor may be normally on. Therefore, the above-described thickness is preferable. Note that the first metal oxide film 402
The second metal oxide film 404 and the oxide semiconductor film 403 are preferably formed successively without being exposed to the air.

As an oxide semiconductor used for the oxide semiconductor film 403, In—which is an oxide of a quaternary metal is used.
Sn—Ga—Zn—O-based oxide semiconductors and In—Ga—Zn— which are oxides of ternary metals
O-based oxide semiconductor, In-Sn-Zn-O-based oxide semiconductor, In-Al-Zn-O-based oxide semiconductor, Sn-Ga-Zn-O-based oxide semiconductor, Al-Ga-Zn-O-based Oxide semiconductors, Sn—Al—Zn—O-based oxide semiconductors, In—Zn—O-based oxide semiconductors that are binary metal oxides, Sn—Zn—O-based oxide semiconductors, Al—Zn— O-based oxide semiconductor, Zn-
Mg-O-based oxide semiconductor, Sn-Mg-O-based oxide semiconductor, In-Mg-O-based oxide semiconductor, In-Ga-O-based oxide semiconductor, In-O-based oxide semiconductor, Sn-O A series oxide semiconductor, a Zn-O series oxide semiconductor, or the like can be used. In addition, Si oxide
O ₂ may be included. Here, for example, an In—Ga—Zn—O-based oxide semiconductor means an oxide film containing indium (In), gallium (Ga), and zinc (Zn), and the composition ratio thereof is not particularly limited. Absent. Moreover, elements other than In, Ga, and Zn may be included.

The oxide semiconductor film 403 can be a thin film represented by the chemical formula, InMO ₃ (ZnO) _m (m> 0). Here, M represents one or more metal elements selected from Ga, Al, Mn, and Co. For example, M includes Ga, Ga and Al, Ga and Mn, or Ga and Co.

In the case where an In—Zn—O-based material is used for the oxide semiconductor film 403, the composition ratio of the target used is an atomic ratio, and In: Zn = 50: 1 to 1: 2 (converted to a molar ratio). Then, In ₂ O ₃ : ZnO = 25: 1 to 1: 4), preferably In: Zn = 20: 1 to 1: 1 (
In ₂ O ₃ : ZnO = 10: 1 to 1: 2) in terms of molar ratio, more preferably In
: Zn = 15: 1 to 1.5: 1 (in terms of molar ratio, In ₂ O ₃ : ZnO = 15: 2
3: 4). For example, a target used to form an In—Zn—O-based oxide semiconductor is
When the atomic ratio is In: Zn: O = X: Y: Z, Z> 1.5X + Y.

In this embodiment, the oxide semiconductor film 403 is formed by a sputtering method with the use of an In—Ga—Zn—O-based target. The oxide semiconductor film 403 can be formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

As a target for forming an In—Ga—Zn—O film as the oxide semiconductor film 403 by a sputtering method, for example, a composition ratio of In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1:
A 1: 1 [molar ratio] target can be used. Without limitation to the material and the composition of the target, for _{example, In 2 O 3: Ga 2} O 3: ZnO = 1: 1: 2 [mol
Number ratio target may be used.

The filling rate of the target is 90% or more and 100% or less, preferably 95% or more and 99.9%.
It is as follows. By using a target with a high filling rate, the oxide semiconductor film 40 is formed.
3 can be a dense film.

As a sputtering gas used for forming the oxide semiconductor film 403, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed is preferably used.

The oxide semiconductor film 403 is formed by holding the substrate 400 in a deposition chamber kept under reduced pressure,
The substrate temperature is 100 ° C. or higher and 600 ° C. or lower, preferably 200 ° C. or higher and 400 ° C. or lower.
By forming the substrate 400 while heating, the concentration of impurities contained in the formed oxide semiconductor film 403 can be reduced. Further, damage due to sputtering is reduced.
Then, a sputtering gas from which hydrogen and water are removed is introduced while moisture remaining in the deposition chamber is removed, and the oxide semiconductor film 403 is formed over the substrate 400 using the above target. In order to remove moisture remaining in the deposition chamber, it is preferable to use an adsorption-type vacuum pump such as a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. In the film formation chamber evacuated using a cryopump, for example, a compound containing a hydrogen atom (more preferably a compound containing a carbon atom) such as a hydrogen atom or water (H ₂ O) is exhausted. The concentration of impurities contained in the oxide semiconductor film 403 formed in the chamber can be reduced.

As an example of film formation conditions, the distance between the substrate and the target is 100 mm, and the pressure is 0.6 Pa.
A condition under a direct current (DC) power supply of 0.5 kW and an oxygen (oxygen flow rate 100%) atmosphere is applied. Note that a pulse direct current power source is preferable because powder substances (also referred to as particles or dust) generated in film formation can be reduced and the film thickness can be made uniform.

After that, heat treatment (first heat treatment) is preferably performed on the oxide semiconductor film 403. By this first heat treatment, excess hydrogen (including water and a hydroxyl group) in the oxide semiconductor film 403 can be removed. Further, the first metal oxide film 4 is formed by the first heat treatment.
02 or excess hydrogen (including water and hydroxyl groups) in the second metal oxide film 404 can be removed. The temperature of the first heat treatment is 250 ° C. or higher and 700 ° C. or lower, preferably 450 ° C.
It is set to be not lower than 600 ° C. and lower than the strain point of the substrate.

In the heat treatment, for example, an object to be processed is introduced into an electric furnace using a resistance heating element, and under a nitrogen atmosphere,
It can be performed at 450 ° C. for 1 hour. During this time, the oxide semiconductor film 403 is not exposed to the air so that water and hydrogen are not mixed.

The heat treatment apparatus is not limited to an electric furnace, and an apparatus for heating an object to be processed by heat conduction or heat radiation from a medium such as a heated gas may be used. For example, GRTA (Gas Rap
id Thermal Anneal) device, LRTA (Lamp Rapid The
RTA (Rapid Thermal Anneal) equipment, etc.
) Device can be used. The LRTA apparatus is an apparatus that heats an object to be processed by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp.
The GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas. As the gas, an inert gas that does not react with an object to be processed by heat treatment, such as nitrogen or a rare gas such as argon, is used.

For example, as the first heat treatment, a GRTA process may be performed in which an object to be processed is put in a heated inert gas atmosphere and heated for several minutes, and then the object to be processed is extracted from the inert gas atmosphere. When GRTA treatment is used, high-temperature heat treatment can be performed in a short time. In addition, application is possible even under temperature conditions exceeding the heat resistance temperature of the object to be processed. Note that the inert gas may be switched to a gas containing oxygen during the treatment. By performing the first heat treatment in an atmosphere containing oxygen,
This is because defect levels in the energy gap due to oxygen vacancies can be reduced.

Note that as the inert gas atmosphere, an atmosphere containing nitrogen or a rare gas (such as helium, neon, or argon) as a main component and not including water, hydrogen, or the like is preferably used. For example, the purity of nitrogen or a rare gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (
That is, the impurity concentration is 1 ppm or less, preferably 0.1 ppm or less.

By the way, the above heat treatment (first heat treatment) has an effect of removing hydrogen, water, and the like.
This heat treatment can also be referred to as dehydration treatment, dehydrogenation treatment, or the like. The dehydration treatment or dehydrogenation treatment can be performed at a timing, for example, after the oxide semiconductor film 403 is processed into an island shape. Further, such dehydration treatment and dehydrogenation treatment are not limited to one time, and may be performed a plurality of times.

The gate insulating film in contact with the oxide semiconductor film 403 (a stack of the first metal oxide film 402 and the second metal oxide film 404) is supplied with oxygen by an oxygen doping treatment or the like,
It has an oxygen excess region. Accordingly, movement of oxygen from the oxide semiconductor film 403 to the gate insulating film can be suppressed. Further, when the oxide semiconductor film 403 is stacked in contact with the gate insulating film to which oxygen is supplied, oxygen can be supplied from the gate insulating film to the oxide semiconductor film 403. Further, as the second metal oxide film 404 in contact with the oxide semiconductor film 403, a gallium aluminum oxide film having an oxygen-excess region is provided, so that the oxide semiconductor film 4
The state of the interface with 03 can be kept good, and the pileup of hydrogen at the interface can be reduced. Further, by providing an aluminum gallium oxide film having an oxygen-excess region as the first metal oxide film 402, entry of water into the oxide semiconductor film 403 can be prevented.

Note that supply of oxygen from the gate insulating film having an oxygen-excess region to the oxide semiconductor film 403 is further accelerated by performing heat treatment in a state where the gate insulating film and the oxide semiconductor film 403 are in contact with each other. . Further, it is preferable that at least part of oxygen added to the gate insulating film and supplied to the oxide semiconductor film 403 have oxygen dangling bonds in the oxide semiconductor. By having dangling bonds, hydrogen is bonded to hydrogen that can remain in the oxide semiconductor film, thereby fixing hydrogen (
This is because non-movable ionization can be performed.

Next, the oxide semiconductor film 403 is preferably processed into an island-shaped oxide semiconductor film 403 by a second photolithography process (FIG. 5B). The island-shaped oxide semiconductor film 403
A resist mask for forming the film may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used. The etching of the oxide semiconductor film 403 here may be dry etching or wet etching, or both of them may be used.

Next, a conductive film for forming a source electrode and a drain electrode (including a wiring formed using the same layer) is formed over the second metal oxide film 404 and the oxide semiconductor film 403.
As the conductive film used for the source electrode and the drain electrode, for example, Al, Cr, Cu, Ta
A metal film containing an element selected from Ti, Mo, W, or a metal nitride film (a titanium nitride film, a molybdenum nitride film, or a tungsten nitride film) containing the above-described element as a component can be used. Also, Ti, Mo, W on one or both of the lower side or the upper side of a metal film such as Al, Cu, etc.
Alternatively, a high melting point metal film such as a metal nitride film (titanium nitride film, molybdenum nitride film, tungsten nitride film) may be stacked. Further, the conductive film used for the source electrode and the drain electrode may be formed using a conductive metal oxide. As the conductive metal oxide, indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), indium oxide tin oxide alloy (In ₂ O ₃ —SnO ₂ , abbreviated as ITO), An indium oxide-zinc oxide alloy (In ₂ O ₃ —ZnO) or a metal oxide material containing silicon oxide can be used.

A resist mask is formed over the conductive film by a third photolithography step, and selective etching is performed to form the source electrode 405a and the drain electrode 405b, and then the resist mask is removed (FIG. 5C). Ultraviolet light, KrF laser light, or ArF laser light is preferably used for light exposure for forming the resist mask in the third photolithography process. The channel length L of a transistor to be formed later is determined by the distance between the lower end portion of the source electrode 405a and the lower end portion of the drain electrode 405b which are adjacent to each other over the oxide semiconductor film 403. Note that in the case of performing exposure with a channel length L of less than 25 nm, for example, when the resist mask is formed in the third photolithography process using extreme ultraviolet (Extreme Ultraviolet) having a very short wavelength of several nm to several tens of nm. It is good to perform exposure. Exposure by extreme ultraviolet light has a high resolution and a large depth of focus. Therefore, the channel length L of a transistor to be formed later can be reduced, and the operation speed of the circuit can be increased.

In order to reduce the number of photomasks used in the photolithography process and the number of processes, the etching process may be performed using a resist mask formed by a multi-tone mask that is an exposure mask in which transmitted light has a plurality of intensities. Good. A resist mask formed using a multi-tone mask has a shape with a plurality of thicknesses, and the shape can be further deformed by etching. Therefore, the resist mask can be used for a plurality of etching processes for processing into different patterns. . Therefore, a resist mask corresponding to at least two kinds of different patterns can be formed by using one multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can be reduced, so that the process can be simplified.

Note that it is preferable that etching conditions be optimized so that the oxide semiconductor film 403 is not etched and divided when the conductive film is etched. However, it is difficult to obtain a condition that only the conductive film is etched and the oxide semiconductor film 403 is not etched at all. When the conductive film is etched, only part of the oxide semiconductor film 403 is etched. In some cases, 5% to 50% of the thickness of the semiconductor film 403 is etched, whereby the oxide semiconductor film 403 having a groove (a depression) is formed.

Next, plasma treatment using a gas such as N ₂ O, N ₂ , or Ar may be performed to remove adsorbed water or the like attached to the exposed surface of the oxide semiconductor film 403. In the case where plasma treatment is performed, it is preferable that the third metal oxide film 407 in contact with the oxide semiconductor film 403 be formed without exposure to the air following the plasma treatment.

The third metal oxide film 407 can be formed using the same material and the same process as the second metal oxide film 404. Note that the second metal oxide film 4 is used to maintain a favorable state of the interface with the oxide semiconductor film and to suppress hydrogen pileup at the interface with the oxide semiconductor film.
Similarly to 04, it is more preferable to use a gallium aluminum oxide film as the third metal oxide film 407.

Next, treatment for supplying oxygen such as oxygen doping treatment is preferably performed on the third metal oxide film 407. Note that when the third metal oxide film 407 is formed by a sputtering method, an oxygen gas or a mixed gas of an inert gas (for example, a rare gas such as argon or nitrogen) and oxygen is introduced. Thus, oxygen may be supplied to the third metal oxide film 407.

Next, a fourth metal oxide film 409 is formed over the third metal oxide film 407 (FIG. 5D
)). In the transistor 330, the third metal oxide film 407 and the fourth metal oxide film 409 function as a gate insulating film (second gate insulating film). The fourth metal oxide film 409 can be formed using the same material and the same process as the first metal oxide film 402. Note that an aluminum gallium oxide film is used as the fourth metal oxide film 409 in order to maintain a favorable state of the interface with the third metal oxide film 407 and to prevent water from entering the oxide semiconductor film. Is more preferable.

Next, treatment for supplying oxygen such as oxygen doping treatment is preferably performed on the fourth metal oxide film 409. Note that when the fourth metal oxide film 409 is formed by a sputtering method, an oxygen gas or an inert gas (for example, a rare gas such as argon or nitrogen) and a mixed gas of oxygen are introduced. Thus, oxygen may be supplied to the fourth metal oxide film 409. Note that the process of supplying oxygen to the fourth metal oxide film 409 is performed using the third metal oxide film 40.
7 may be combined with the process of supplying oxygen to the gas.

Next, second heat treatment is preferably performed in a state where the oxide semiconductor film 403 is partly in contact with the third metal oxide film 407 (a channel formation region). The temperature of the second heat treatment is 250 ° C. or higher and 7
00 ° C. or lower, preferably 450 ° C. or higher and 600 ° C. or lower, or lower than the strain point of the substrate.

The second heat treatment is performed using nitrogen, oxygen, ultra-dry air (water content is 20 ppm or less, preferably 1
ppm or less, more preferably 10 ppb or less) or a rare gas (argon, helium, etc.) atmosphere, but water, hydrogen, etc. in the atmosphere of nitrogen, oxygen, ultra-dry air, or rare gas. Is preferably not included. Nitrogen introduced into the heat treatment apparatus,
The purity of oxygen or a rare gas is 6N (99.9999%) or more, preferably 7N (99.9).
999%) or more (that is, the impurity concentration is 1 ppm or less, preferably 0.1 ppm or less).

In the second heat treatment, heating is performed in a state where the oxide semiconductor film 403 is in contact with the second metal oxide film 404 and the third metal oxide film 407 each having an oxygen-excess region. Therefore, the second metal oxide film containing oxygen is used as oxygen, which is one of the main component materials of the oxide semiconductor that may be simultaneously reduced by the above-described dehydration (or dehydrogenation) treatment. 4
04 and the third metal oxide film 407 can be supplied to the oxide semiconductor film 403. Accordingly, charge trapping centers in the oxide semiconductor film 403 can be reduced. Through the above steps, the oxide semiconductor film 4 is highly purified and electrically i-type (intrinsic).
03 can be formed. Further, this heat treatment can remove impurities from the first to fourth metal oxide films at the same time, and can be highly purified.

Note that in this embodiment, the second heat treatment is performed after the formation of the fourth metal oxide film 409; however, the timing of the second heat treatment is after the formation of the third metal oxide film 407. This is not particularly limited. For example, the second heat treatment may be performed after the third metal oxide film 407 is formed.

As described above, by applying the first heat treatment and the second heat treatment, the oxide semiconductor film 403 is used.
Can be highly purified so that impurities other than its main component are not contained as much as possible. In the highly purified oxide semiconductor film 403, the number of carriers derived from donors is extremely small (near zero), and the carrier concentration is less than 1 × 10 ¹⁴ / cm ³ , preferably less than 1 × 10 ¹² / cm ³ , More preferably, it is less than 1 × 10 ¹¹ / cm ³ .

Next, the conductive layer 410 is provided over the fourth metal oxide film 409 and in a region overlapping with the channel formation region of the oxide semiconductor film 403, whereby the transistor 330 illustrated in FIG.
Can be formed. The conductive layer 410 can function as the second gate electrode and can be formed using the same material and the same process as the gate electrode 401. Note that in the case where the conductive layer 410 is used as the second gate electrode, the third metal oxide film 407 and the fourth gate electrode are used.
A stacked film made of the metal oxide film 409 functions as a second gate insulating film.

The conductive layer 410 functions as a second gate electrode, and the conductive layer 410 is used as the oxide semiconductor film 40.
3 in a position overlapping with the channel formation region 3, the amount of change in the threshold voltage of the transistor 330 before and after the BT test in a bias-thermal stress test (hereinafter referred to as a BT test) for examining the reliability of the transistor 330. Can be further reduced.
Note that the potential of the second gate electrode may be the same as or different from that of the gate electrode 401 (first gate electrode). Further, the potential of the second gate electrode may be GND, 0 V, or a floating state.

Through the above process, the transistor 330 is formed. The transistor 330 is a transistor including the highly purified oxide semiconductor film 403 which intentionally excludes impurities such as hydrogen, water, a hydroxyl group, or hydride (also referred to as a hydrogen compound) from the oxide semiconductor film 403. Further, by providing the first to fourth metal oxide films, impurities such as water and hydrogen can be mixed again into the oxide semiconductor film 403 or oxygen can be released from the oxide semiconductor film 403 and the interface. It can be reduced or prevented. Thus, the transistor 330 is electrically stable because variation in electrical characteristics is suppressed.

Note that although not illustrated, a protective insulating film may be further formed so as to cover the transistor 330. As the protective insulating film, a silicon nitride film, a silicon nitride oxide film, an aluminum nitride film, or the like can be used.

Further, a planarization insulating film may be provided over the transistor 330. As the planarization insulating film, an organic material having heat resistance such as acrylic, polyimide, benzocyclobutene, polyamide, or epoxy can be used. In addition to the organic material, a low dielectric constant material (low-k material), a siloxane resin, PSG (phosphorus glass), BPSG (phosphorus boron glass), or the like can be used. Note that a plurality of insulating films formed using these materials may be stacked.

<Manufacturing Process of Transistor 320>
An example of a manufacturing process of the transistor 320 illustrated in FIGS. 2A to 2C will be described with reference to FIGS. Note that the manufacturing process of the transistor 320 is mostly performed in the transistor 3.
30. Therefore, in the following, description of the overlapping part may be omitted.

First, the first metal oxide film 402 is formed over the substrate 400 having an insulating surface. after that,
It is preferable to perform treatment for supplying oxygen, such as oxygen doping treatment, on the first metal oxide film 402.

Note that an insulating film serving as a base film may be provided between the substrate 400 and the first metal oxide film 402. The base film has a function of preventing diffusion of impurity elements from the substrate 400, and has a stacked structure of one or more films selected from a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, and a silicon oxynitride film. Can be formed.

Next, a second metal oxide film 404 is formed over the first metal oxide film 402 (FIG. 6A).
)). After the second metal oxide film 404 is formed, treatment for supplying oxygen such as oxygen doping treatment is preferably performed. Note that the oxygen supply process for the first metal oxide film 402 may be combined with the oxygen supply process for the second metal oxide film 404.

Next, the oxide semiconductor film 403 is formed over the second metal oxide film 404, and the oxide semiconductor film 403 is processed into an island shape (FIG. 6B).

Note that heat treatment (dehydration treatment or dehydrogenation treatment) is preferably performed after the oxide semiconductor film 403 is formed or after the oxide semiconductor film 403 is processed into an island shape. The details are similar to those of the transistor 330.

Next, a conductive film for forming a source electrode and a drain electrode (including a wiring formed using the same layer) is formed over the oxide semiconductor film 403, the conductive film is processed, and the source electrode 405a Then, a drain electrode 405b is formed (FIG. 6C).

Next, the source electrode 405a and the drain electrode 405b are covered, and the oxide semiconductor film 4
A third metal oxide film 407 is formed so as to be in contact with part of 03. After that, it is preferable to perform oxygen supply treatment such as oxygen doping treatment on the third metal oxide film 407.

Next, a fourth metal oxide film 409 is formed over the third metal oxide film 407, and gate insulation including a stack of the third metal oxide film 407 and the fourth metal oxide film 409 is formed. A film is formed (FIG. 6D). Note that after the fourth metal oxide film 409 is formed, treatment for supplying oxygen such as oxygen doping is preferably performed. Further, the oxygen supply process for the third metal oxide film 407 may be combined with the oxygen supply process for the fourth metal oxide film 409.

In addition, heat treatment is preferably performed after the oxygen supply treatment is performed on the third metal oxide film 407. Through the heat treatment, oxygen can be supplied to the oxide semiconductor film 403 from at least one of the second metal oxide film 404 and the third metal oxide film 407 containing oxygen.

Next, a conductive film is formed over the fourth metal oxide film 409, and the conductive film is processed to form the gate electrode 414. The gate electrode 414 corresponds to the gate electrode 4 in the transistor 330.
It can be formed by the same material and the same process as 01.

Through the above steps, the transistor 320 can be formed (FIG. 6E).

As described above, as described in this embodiment, using a material including a Group 13 element and oxygen,
By forming the insulating film in contact with the oxide semiconductor film, the state of the interface between the oxide semiconductor film and the insulating film can be kept favorable.

In particular, when the insulating film in contact with the oxide semiconductor film is a gallium oxide film or a gallium aluminum oxide film that has a high gallium content, hydrogen is piled up at the interface between the insulating film and the oxide semiconductor film. Can be effectively suppressed. Furthermore, the insulating film in contact with the oxide semiconductor film has a stacked structure, and is in contact with the gallium oxide film or the gallium aluminum oxide film (that is, outside the oxide semiconductor film) and is a film containing a large amount of aluminum. By providing a film or the like, water can be prevented from entering the oxide semiconductor film. In addition, by providing a film containing aluminum above and below the oxide semiconductor film and further bringing the film containing aluminum into close contact with each other, the effect of preventing entry of water can be further improved.

In addition, since the insulating film in contact with the oxide semiconductor film includes a region where oxygen is higher than the stoichiometric composition ratio, the oxide semiconductor film may be simultaneously reduced by dehydration (or dehydrogenation) treatment of the oxide semiconductor film. A certain amount of oxygen can be supplied to the oxide semiconductor film. Accordingly, oxygen defects in the oxide semiconductor film can be reduced, so that charge trapping centers in the oxide semiconductor film can be reduced. Through the above steps, an oxide semiconductor film which is highly purified and electrically i-type (intrinsic) can be formed.

In the semiconductor device according to one embodiment of the present invention, the off-state current density of the transistor is 10 zA / μm or less depending on the voltage between the source electrode and the drain electrode by using a highly purified oxide semiconductor film as an active layer. , Preferably 1 zA / μm or less, more preferably 1 yA / μm
It can be: Therefore, a transistor using a highly purified oxide semiconductor film as an active layer has a significantly lower off-state current than a transistor using crystalline silicon.

In addition, the use of a highly purified oxide semiconductor can significantly reduce the temperature dependence of off-state current of the transistor. This is because impurities that become electron donors (donors) in the oxide semiconductor are removed, and the oxide semiconductor is highly purified, so that the conductivity type approaches the intrinsic type as much as possible, and the Fermi level is in the forbidden band. It can be said that it is located in the center. This is also because the energy gap of the oxide semiconductor is 3 eV or more and the number of thermally excited carriers is extremely small. Moreover, the fact that the source electrode and the drain electrode are in a degenerated state is also a factor for reducing the temperature dependence. Most of the operation of the transistor is due to carriers injected from the degenerated source electrode into the oxide semiconductor, and the carrier density has no temperature dependence, so that the temperature dependence of off-state current can be significantly reduced. Can be explained.

In the oxide semiconductor film in which the hydrogen concentration is sufficiently reduced to be highly purified and the defect level in the energy gap due to oxygen deficiency is reduced by supplying sufficient oxygen, the carrier concentration is sufficiently low, By using such an oxide semiconductor film as an active layer, a shift in threshold voltage can be suppressed and the transistor can be normally off.

As described above, according to one embodiment of the present invention, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

(Embodiment 2)
A semiconductor device (also referred to as a display device) having a display function can be manufactured using the transistor exemplified in Embodiment 1. In addition, part or the whole of a driver circuit including a transistor can be formed over the same substrate as the pixel portion to form a system-on-panel.

In FIG. 7A, a sealant 4005 is provided so as to surround the pixel portion 4002 provided over the first substrate 4001 and is sealed with the second substrate 4006. FIG.
In A), a scan line driver formed using a single crystal semiconductor film or a polycrystalline semiconductor film over a separately prepared substrate in a region different from the region surrounded by the sealant 4005 over the first substrate 4001. A circuit 4004 and a signal line driver circuit 4003 are mounted. Further, a signal line driver circuit 4003 which is separately formed, and various signals and potentials supplied to the scan line driver circuit 4004 or the pixel portion 4002 are FPC (Flexible printed circuit).
) 4018a and 4018b.

7B and 7C, the pixel portion 4002 provided over the first substrate 4001
A sealant 4005 is provided so as to surround the scan line driver circuit 4004.
A second substrate 4006 is provided over the pixel portion 4002 and the scan line driver circuit 4004. Therefore, the pixel portion 4002 and the scan line driver circuit 4004 are sealed together with the display element by the first substrate 4001, the sealant 4005, and the second substrate 4006. FIG.
7B and 7C, a single crystal semiconductor film or a polycrystalline semiconductor film is formed over a separately prepared substrate in a region different from the region surrounded by the sealant 4005 over the first substrate 4001. A signal line driver circuit 4003 formed in (1) is mounted. 7B and 7C
), A signal line driver circuit 4003 which is separately formed, and various signals and potentials supplied to the scan line driver circuit 4004 or the pixel portion 4002 are supplied from an FPC 4018.

In FIG. 7B and FIG. 7C, a signal line driver circuit 4003 is formed separately, and the first
Although the example mounted on the substrate 4001 is shown, it is not limited to this configuration. The scan line driver circuit may be separately formed and then mounted, or only part of the signal line driver circuit or part of the scan line driver circuit may be separately formed and then mounted.

Note that a connection method of a separately formed drive circuit is not particularly limited, and COG (Ch
ip On Glass) method, wire bonding method, or TAB (Tape A)
(automated bonding) method or the like can be used. FIG. 7A shows C
In this example, the signal line driver circuit 4003 and the scanning line driver circuit 4004 are mounted by the OG method.
FIG. 7B illustrates an example in which the signal line driver circuit 4003 is mounted by a COG method.
) Is an example in which the signal line driver circuit 4003 is mounted by a TAB method.

The display device includes a panel in which the display element is sealed, and a module in which an IC including a controller is mounted on the panel.

Note that a display device in this specification means an image display device, a display device, or a light source (including a lighting device). Further, an IC (integrated circuit) is directly mounted on a connector, for example, a module with an FPC or TAB tape or TCP attached, a module with a printed wiring board provided on the end of the TAB tape or TCP, or a display element by the COG method. All modules are included in the display device.

The pixel portion and the scan line driver circuit provided over the first substrate include a plurality of transistors, and the transistor described as an example in Embodiment 1 can be used.

As a display element provided in the display device, a liquid crystal element (also referred to as a liquid crystal display element), a light-emitting element (
A light-emitting display element). A light-emitting element includes an element whose luminance is controlled by current or voltage, specifically, an inorganic EL (Electro Electrode).
Luminescence), organic EL, and the like. In addition, a display medium whose contrast is changed by an electric effect, such as electronic ink, can be used.

One mode of a semiconductor device is described with reference to FIGS. 8 to 10 correspond to cross-sectional views taken along line MN in FIG. 7B.

As shown in FIGS. 8 to 10, the semiconductor device includes a connection terminal electrode 4015 and a terminal electrode 4016.
The connection terminal electrode 4015 and the terminal electrode 4016 are electrically connected to a terminal included in the FPC 4018 through an anisotropic conductive film 4019.

The connection terminal electrode 4015 is formed using the same conductive film as the first electrode layer (first electrode) 4030, and the terminal electrode 4016 is formed using the same conductive film as the source and drain electrodes of the transistors 4010 and 4011. Yes.

In addition, the pixel portion 4002 provided over the first substrate 4001 and the scan line driver circuit 4004 include
8 to 10 illustrate a transistor 4010 included in the pixel portion 4002 and a transistor 4011 included in the scan line driver circuit 4004.

In this embodiment, the transistor 4010 and the transistor 4011 are described as Embodiment 1
The transistor shown by can be applied. 8 to 10 illustrate an example in which the transistor 330 described in Embodiment 1 is used, this embodiment is not limited to this, and the transistors 310, 320, 340, 350, 360, 370
380 or 390 can be used as appropriate. In addition, the transistor 4010 and the transistor 4011 do not necessarily have the same structure. The transistor 4010 and the transistor 4011 are electrically stable because variations in electrical characteristics are suppressed. Therefore, a highly reliable semiconductor device can be provided as the semiconductor device of this embodiment illustrated in FIGS.

A transistor 4010 provided in the pixel portion 4002 is electrically connected to a display element to form a display panel. The display element is not particularly limited as long as display can be performed, and various display elements can be used.

FIG. 8 shows an example of a liquid crystal display device using a liquid crystal element as a display element. In FIG. 8, a liquid crystal element 4013 which is a display element includes a first electrode layer 4030 and a second electrode layer (second electrode) 40.
31 and a liquid crystal layer 4008. Note that insulating films 4032 and 4033 functioning as alignment films are provided so as to sandwich the liquid crystal layer 4008. The second electrode layer 4031 is provided on the second substrate 4006 side, and the first electrode layer 4030 and the second electrode layer 4031 are the liquid crystal layer 40.
It is the structure which laminates | stacks through 08.

4035 is a columnar spacer obtained by selectively etching the insulating film,
It is provided to control the film thickness (cell gap) of the liquid crystal layer 4008. A spherical spacer may be used.

When a liquid crystal element is used as the display element, a thermotropic liquid crystal, a low molecular liquid crystal, a polymer liquid crystal, a polymer dispersed liquid crystal, a ferroelectric liquid crystal, an antiferroelectric liquid crystal, or the like can be used. These liquid crystal materials exhibit a cholesteric phase, a smectic phase, a cubic phase, a chiral nematic phase, an isotropic phase, and the like depending on conditions.

Alternatively, a liquid crystal exhibiting a blue phase for which an alignment film is unnecessary may be used. The blue phase is one of the liquid crystal phases. When the temperature of the cholesteric liquid crystal is increased, the blue phase appears immediately before the transition from the cholesteric phase to the isotropic phase. Since the blue phase appears only in a narrow temperature range, in order to improve the temperature range, a liquid crystal composition mixed with 5% by weight or more of a chiral agent is used for the liquid crystal layer.
A liquid crystal composition containing a liquid crystal exhibiting a blue phase and a chiral agent has a response speed as short as 1 msec or less and is optically isotropic, so alignment treatment is unnecessary and viewing angle dependence is small. Further, since it is not necessary to provide an alignment film, a rubbing process is not required, so that electrostatic breakdown caused by the rubbing process can be prevented, and defects or breakage of the liquid crystal display device during the manufacturing process can be reduced. . Therefore, the productivity of the liquid crystal display device can be improved.

The specific resistivity of the liquid crystal material is 1 × 10 ⁹ Ω · cm or more, preferably 1 × 10 ^1.
1 Ω · cm or more, more preferably 1 × 10 ¹² Ω · cm or more. In addition, the value of the specific resistivity in this specification shall be the value measured at 20 degreeC.

The size of the storage capacitor provided in the liquid crystal display device is set so that charges can be held for a predetermined period in consideration of a leakage current of a transistor arranged in the pixel portion. By using a transistor including a high-purity oxide semiconductor film, it is sufficient to provide a storage capacitor having a capacity of 1/3 or less, preferably 1/5 or less of the liquid crystal capacity of each pixel. .

In the transistor including the highly purified oxide semiconductor film used in this embodiment, the current value in an off state (off-state current value) can be reduced. Therefore, the holding time of an electric signal such as an image signal can be increased, and the writing interval can be set longer in the power-on state. Therefore, since the frequency of the refresh operation can be reduced, there is an effect of suppressing power consumption.

In addition, the transistor including the highly purified oxide semiconductor film used in this embodiment can have a relatively high field-effect mobility and can be driven at high speed. Therefore, a high-quality image can be provided by using the transistor in the pixel portion of the liquid crystal display device. In addition, since the transistor can be manufactured separately over the same substrate in a driver circuit portion or a pixel portion, the number of parts of the liquid crystal display device can be reduced.

Liquid crystal display devices include TN (Twisted Nematic) mode, IPS (In-P
lane-Switching) mode, FFS (Fringe Field Switch)
ching) mode, ASM (Axial Symmetrical aligned)
Micro-cell mode, OCB (Optical Compensated B)
irefringence mode, FLC (Ferroelectric Liquid)
d Crystal) mode, AFLC (Antiferroelectric Liq)
uid Crystal) mode or the like can be used.

Alternatively, a normally black liquid crystal display device such as a transmissive liquid crystal display device employing a vertical alignment (VA) mode may be used. Here, the vertical alignment mode is a type of method for controlling the alignment of liquid crystal molecules of the liquid crystal display panel, and is a method in which the liquid crystal molecules are oriented in the vertical direction with respect to the panel surface when no voltage is applied. There are several examples of the vertical alignment mode. For example, MVA (Multi-Domain Vertical Alignment)
nt) mode, PVA (Patterned Vertical Alignment)
Mode, ASV mode, and the like can be used. Further, a method called multi-domain or multi-domain design in which pixels (pixels) are divided into several regions (sub-pixels) and molecules are tilted in different directions can be used.

In the display device, a black matrix (light shielding layer), a polarizing member, a retardation member, an optical member (an optical substrate) such as an antireflection member, and the like are provided as appropriate. For example, circularly polarized light using a polarizing substrate and a retardation substrate may be used. Further, a backlight, a sidelight, or the like may be used as the light source.

It is also possible to perform a time division display method (field sequential drive method) using a plurality of light emitting diodes (LEDs) as a backlight. By applying the field sequential driving method, color display can be performed without using a color filter.

As a display method in the pixel portion, a progressive method, an interlace method, or the like can be used. Further, the color elements controlled by the pixels when performing color display are not limited to three colors of RGB (R represents red, G represents green, and B represents blue). For example, RGBW (W represents white)
In addition, there are RGB colors in which one or more colors of yellow, cyan, magenta, and the like are added. In addition,
The size of the display area may be different for each dot of the color element. However, the present invention is not limited to a display device for color display, and can also be applied to a display device for monochrome display.

FIG. 12A is a plan view of one pixel in a liquid crystal display device to which the transistor 310 described in Embodiment 1 is applied. FIG. 12B is a cross-sectional view taken along line X1-X2 in FIG.

In FIG. 12A, a plurality of source wirings (including a source electrode 405a) are parallel to each other (
They are arranged in a state of extending in the vertical direction in FIG. The plurality of gate wirings (including the gate electrode 401) are arranged so as to extend in a direction substantially orthogonal to the source wiring (left and right direction in the drawing) and to be separated from each other. The capacitor wiring 408 is disposed at a position adjacent to each of the plurality of gate wirings, and extends in a direction substantially parallel to the gate wiring, that is, in a direction substantially orthogonal to the source wiring (left-right direction in the drawing). A substantially rectangular space is surrounded by the source wiring, the capacitor wiring 408, and the gate wiring, and the pixel electrode and the common electrode of the liquid crystal display device are arranged in this space via the liquid crystal layer 444. The transistor 310 for driving the pixel electrode is arranged at the upper left corner in the drawing. A plurality of pixel electrodes and transistors are arranged in a matrix.

In the liquid crystal display device in FIG. 12, the first electrode 44 that is electrically connected to the transistor 310.
6 functions as a pixel electrode, and the second electrode 447 functions as a common electrode. In addition, an alignment film may be provided between the first electrode 446 and the liquid crystal layer 444 or between the second electrode 447 and the liquid crystal layer 444. 12 includes the first electrode 446 and the second electrode.
In the region where the electrode 447 does not overlap, the light shielding layer 450 is formed on the second substrate 442 side which is the counter substrate.
(Black matrix) is provided. The second substrate 442 is provided with an insulating layer 455 over the light-blocking layer 450.

Note that the light-blocking layer 450 is formed inside the pair of substrates (the liquid crystal layer 4) that is fixed with the liquid crystal layer 444 interposed therebetween.
44 side) or outside the substrate (on the opposite side of the liquid crystal layer 444).

The transistor 310 includes a gate electrode 401, a gate insulating film having a stacked structure of a first metal oxide film 402 and a second metal oxide film 404, an oxide semiconductor film 403, a source electrode 405a, and a drain electrode. 405b, a third metal oxide film 407, and a fourth metal oxide film 409. Further, an interlayer film 417 is formed over the transistor 310.

Although not shown, a backlight, a sidelight, or the like can be used as a light source. Light from the light source is from the first substrate 441 side which is an element substrate to the second substrate 44 which is the viewing side.
Irradiate to 2 through.

In FIG. 12, the polarizing plate 4 is placed outside the first substrate 441 (on the side opposite to the liquid crystal layer 444).
A polarizing plate 443b is provided on the outer side of the second substrate 442 (on the side opposite to the liquid crystal layer 444).

In the structure illustrated in FIG. 12, the gate electrode 401 is disposed so as to cover the lower side of the oxide semiconductor film 403, and the light shielding layer 450 is disposed so as to cover the upper side of the oxide semiconductor film 403. Therefore, the transistor 310 can have a structure in which light can be blocked on the upper side and the lower side. By the light shielding, deterioration of transistor characteristics can be reduced.

FIG. 13A is a plan view in which part of one pixel in another liquid crystal display device to which the transistor 310 described in Embodiment 1 is applied is enlarged. Further, FIG. 13B is the same as FIG.
Is a cross-sectional view taken along line Y1-Y2.

In the liquid crystal display device in FIG. 13, a plurality of pixels are provided in a matrix, and the transistor 310 including the oxide semiconductor film described in Embodiment 1 in the pixel, a light-blocking layer 451, and a planarization film are provided. In addition, an interlayer film 417, a first electrode 446 used as a pixel electrode, and a liquid crystal layer 444 are provided over the pixel electrode. Note that FIG. 13 illustrates an example in which the bottom-gate transistor 310 described in Embodiment 1 is used; however, this embodiment is not limited thereto.

In FIG. 13, at least the oxide semiconductor film 40 covers the transistor 310.
3 is provided with a light shielding layer 451 (black matrix). Light shielding layer 45
1 can block light from entering the oxide semiconductor film 403 of the transistor 310, and thus has an effect of preventing and stabilizing a change in electrical characteristics of the transistor 310 due to light sensitivity of the oxide semiconductor film 403. In addition, since the light-blocking layer 451 can prevent light leakage to adjacent pixels, display with higher contrast and higher definition can be performed. Therefore, high definition and high reliability of the liquid crystal display device can be achieved.

A light shielding layer may be further formed on the counter substrate side of the liquid crystal display device. In that case, the effect of improving the contrast and stabilizing the transistor can be enhanced. When the light-blocking layer is formed on the counter substrate side, if it is formed in a region corresponding to the transistor through the liquid crystal layer (at least a region overlapping with the semiconductor layer of the transistor), variation in electric characteristics of the transistor due to light incident from the counter substrate Can be prevented more.

The light-blocking layer 451 uses a material that reflects or absorbs light and has a light-blocking property. For example, a black organic resin can be used, and it may be formed by mixing a pigment-based black resin, carbon black, titanium black, or the like with a resin material such as photosensitive or non-photosensitive polyimide. A light-shielding metal film can also be used, for example, chromium, molybdenum, nickel, titanium,
Cobalt, copper, tungsten, aluminum, or the like may be used.

The formation method of the light shielding layer 451 is not particularly limited, and may be an evaporation method, a sputtering method, a CVD method, depending on the material.
Etching method (dry etching or wet etching) as necessary using dry methods such as spin coating, or wet methods such as spin coating, dipping, spray coating, and droplet discharge methods (inkjet method, screen printing, offset printing, etc.) Can be processed into a desired pattern.

As shown in FIG. 13, in the case where the light shielding layer is formed as a part of the interlayer film 417, there is no problem of error in alignment between the light shielding layer and the pixel region, and the formation region can be controlled more precisely and finely Pattern pixels can also be handled. Further, by providing the light shielding layer 451 on the first substrate 441 side, the light irradiated from the counter substrate side is absorbed and blocked by the light shielding layer 451 when the liquid crystal layer 444 is irradiated with light for stabilizing the polymer. Therefore, the entire liquid crystal layer 444 can be irradiated uniformly. Therefore, it is possible to prevent liquid crystal alignment disorder due to non-uniform photopolymerization and display unevenness associated therewith.

Further, as shown in FIGS. 14A and 14B, the light shielding layer 451 and the interlayer film 417 are used.
In the region overlapping with the channel formation region of the oxide semiconductor film 403, the first electrode 4
A conductive layer 420 formed of the same layer as 46 may be formed. The conductive layer 420 can function as a second gate electrode. Note that FIG. 14B shows the line Z1-Z in FIG.
FIG.

13 and 14, the gate electrode 401 is disposed so as to cover the lower side of the oxide semiconductor film 403, and the light shielding layer 451 is disposed so as to cover the upper side of the oxide semiconductor film 403. The Therefore, the transistor can have a structure capable of blocking light on the upper side and the lower side. Accordingly, the stray light irradiation to the oxide semiconductor film 403 can be reduced to about 1/10, preferably about 1/10 of the case where the light-blocking layer is not provided. Further, deterioration of transistor characteristics can be reduced by the light shielding.

In the structure illustrated in FIG. 14, the conductive layer 420 is provided in a position overlapping with the channel formation region of the oxide semiconductor film 403, so that in the BT test for examining the reliability of the transistor, the transistor performance before and after the BT test is measured. The amount of change in threshold voltage can be further reduced.

Moreover, a chromatic translucent resin layer can also be used for the interlayer film. 15A and 15
FIG. 5B illustrates a liquid crystal display device in which the transistor 310 described in Embodiment 1 is applied and a chromatic light-transmitting resin layer is used for an interlayer film. Note that FIG. 15B shows a line W1-W2 in FIG.
FIG.

The liquid crystal display device in FIG. 15 includes a plurality of pixels provided in a matrix, a transistor 310 including an oxide semiconductor film in the pixel, an interlayer film 452 over the transistor, an insulating layer 453 over the interlayer film 452, A first electrode 446 functioning as a pixel electrode is provided over the insulating layer 453 and a liquid crystal layer 444 is provided over the pixel electrode, and the interlayer film 452 is a chromatic light-transmitting resin layer.

The transistor 310 includes a gate electrode 401, a gate insulating film including a first metal oxide film 402 and a second metal oxide film 404, an oxide semiconductor film 403, and a source electrode 405a.
A drain electrode 405b, a third metal oxide film 407, and a fourth metal oxide film 409.
And including.

In the liquid crystal display device in FIG. 15, a chromatic light-transmitting resin layer is used for the interlayer film 452 as a film having a function of attenuating the light intensity of transmitted visible light. The visible light transmittance of the chromatic color light-transmitting resin layer is lower than the visible light transmittance of the oxide semiconductor film 403.

When a colored layer of a chromatic light-transmitting resin layer is used as the interlayer film 452 provided over the transistor 310, the oxide semiconductor film 403 of the transistor 310 without reducing the aperture ratio of the pixel.
The intensity of light incident on the transistor 310 can be attenuated, and the effect of preventing and stabilizing the electrical characteristics of the transistor 310 due to the photosensitivity of the oxide semiconductor can be obtained. Moreover, the chromatic translucent resin layer can function as a color filter layer. When the color filter layer is provided on the counter substrate side, it is difficult to accurately align the pixel region with the element substrate on which the transistor is formed, which may impair image quality. Since it is formed, it is possible to control the formation region more precisely, and it is possible to deal with fine pattern pixels. Further, since the interlayer film and the color filter layer are also used as the same insulating layer, the process can be simplified and a liquid crystal display device can be manufactured at a lower cost.

The chromatic color is a color excluding achromatic colors such as black, gray, and white, and the colored layer is formed of a material that transmits only the colored chromatic light in order to function as a color filter. As the chromatic color, red, green, blue, or the like can be used. Also, cyan, magenta, yellow (
Yellow) or the like may be used. To transmit only colored chromatic light means that light transmitted through the colored layer has a peak at the wavelength of the chromatic light.

Since the chromatic translucent resin layer functions as a colored layer (color filter), the optimum film thickness may be appropriately controlled in consideration of the relationship between the concentration of the coloring material to be included and the light transmittance. When laminating the interlayer film 452 with a plurality of thin films, if at least one layer is a chromatic color transparent resin layer,
It can function as a color filter.

When the film thickness of the chromatic color translucent resin layer differs depending on the chromatic color, or when the light shielding layer or the unevenness caused by the transistor is present, light having a wavelength in the visible light region is transmitted (so-called colorless and transparent).
An insulating layer may be stacked to planarize the interlayer film surface. When the flatness of the interlayer film is increased, the coverage of the pixel electrode and common electrode formed on the interlayer film is improved, and the gap (film thickness) of the liquid crystal layer can be made uniform. To improve image quality.

Although not shown in FIGS. 12 to 15, an alignment film, an optical film such as a phase difference plate or an antireflection film, and the like are appropriately provided. For example, circularly polarized light using a polarizing plate and a retardation plate may be used.

In addition, as a display element included in the display device, a light-emitting element utilizing electroluminescence can be used. A light-emitting element using electroluminescence is distinguished depending on whether the light-emitting material is an organic compound or an inorganic compound. In general, the former is organic E
The L element, the latter is called an inorganic EL element.

In the organic EL element, by applying a voltage to the light emitting element, electrons and holes are respectively injected from the pair of electrodes into the layer containing the light emitting organic compound, and a current flows. Then, these carriers (electrons and holes) recombine, whereby the light-emitting organic compound forms an excited state, and emits light when the excited state returns to the ground state. Due to such a mechanism, such a light-emitting element is referred to as a current-excitation light-emitting element.

Inorganic EL elements are classified into a dispersion-type inorganic EL element and a thin-film inorganic EL element depending on the element structure. The dispersion-type inorganic EL element has a light-emitting layer in which particles of a light-emitting material are dispersed in a binder, and the light emission mechanism is donor-acceptor recombination light emission using a donor level and an acceptor level. The thin-film inorganic EL element has a light emitting layer sandwiched between dielectric layers,
Furthermore, it has a structure in which it is sandwiched between electrodes, and the light emission mechanism is localized light emission that utilizes inner-shell electron transition of metal ions. Note that description is made here using an organic EL element as a light-emitting element.

In order to extract light emitted from the light-emitting element, at least one of the pair of electrodes may be transparent. Then, a transistor and a light emitting element are formed over the substrate, and a top emission that extracts light from a surface opposite to the substrate, a bottom emission that extracts light from a surface on the substrate side, and a surface opposite to the substrate side and the substrate. There is a light-emitting element having a dual emission structure in which light emission is extracted from the light-emitting element, and any light-emitting element having an emission structure can be applied.

FIG. 9 illustrates an example of a light-emitting device using a light-emitting element as a display element. Light-emitting element 4 which is a display element
Reference numeral 513 is electrically connected to a transistor 4010 provided in the pixel portion 4002.
Note that although the structure of the light-emitting element 4513 is a stacked structure of the first electrode layer 4030, the electroluminescent layer 4511, and the second electrode layer 4031, it is not limited to the structure shown. The structure of the light-emitting element 4513 can be changed as appropriate depending on the direction in which light is extracted from the light-emitting element 4513, or the like.

A partition wall 4510 is formed using an organic insulating material or an inorganic insulating material. In particular, a photosensitive resin material is preferably used so that an opening is formed over the first electrode layer 4030 and the side wall of the opening has an inclined surface formed with a continuous curvature.

The electroluminescent layer 4511 may be composed of a single layer or a plurality of layers stacked.

The second electrode layer 4 is used so that oxygen, hydrogen, water, carbon dioxide, or the like does not enter the light-emitting element 4513.
A protective film may be formed over 031 and the partition wall 4510. As the protective film, a silicon nitride film, a silicon nitride oxide film, a DLC film, or the like can be formed. In addition, the first substrate 4001
In the space sealed by the second substrate 4006 and the sealant 4005, a filler 451 is provided.
4 is provided and sealed. Thus, it is preferable to package (enclose) with a protective film (bonded film, ultraviolet curable resin film, etc.) or a cover material that has high air tightness and little degassing so as not to be exposed to the outside air.

As the filler 4514, an ultraviolet curable resin or a thermosetting resin can be used in addition to an inert gas such as nitrogen or argon. PVC (polyvinyl chloride), acrylic resin, polyimide, epoxy resin, silicone resin, PVB ( Polyvinyl butyral) or EVA
(Ethylene vinyl acetate) can be used. For example, nitrogen may be used as the filler.

In addition, if necessary, a polarizing plate or a circularly polarizing plate (including an elliptical polarizing plate) on the emission surface of the light emitting element,
An optical film such as a retardation plate (λ / 4 plate, λ / 2 plate) or a color filter may be provided as appropriate. Further, an antireflection film may be provided on the polarizing plate or the circularly polarizing plate. For example, anti-glare treatment can be performed that diffuses reflected light due to surface irregularities and reduces reflection.

In addition, as a display device, electronic paper that drives electronic ink can be provided. Electronic paper is also called an electrophoretic display device (electrophoretic display), and has the same readability as paper, low power consumption compared to other display devices, and the advantage that it can be made thin and light. ing.

The electrophoretic display device may have various forms, and a plurality of microcapsules including first particles having a positive charge and second particles having a negative charge are dispersed in a solvent or a solute. By applying an electric field to the microcapsule, the particles in the microcapsule are moved in opposite directions to display only the color of the particles assembled on one side. Note that the first particle or the second particle contains a dye and does not move in the absence of an electric field. In addition, the color of the first particles and the color of the second particles are different (including colorless).

As described above, the electrophoretic display device is a display using a so-called dielectrophoretic effect in which a substance having a high dielectric constant moves to a high electric field region.

A solution in which the above microcapsules are dispersed in a solvent is referred to as electronic ink. This electronic ink can be printed on a surface of glass, plastic, cloth, paper, or the like. Color display is also possible by using particles having color filters or pigments.

Note that the first particle and the second particle in the microcapsule are a conductor material, an insulator material,
A material selected from semiconductor materials, magnetic materials, liquid crystal materials, ferroelectric materials, electroluminescent materials, electrochromic materials, and magnetophoretic materials, or a composite material thereof may be used.

In addition, a display device using a twisting ball display system can be used as the electronic paper. The twist ball display method is a method in which spherical particles separately painted in white and black are arranged between a first electrode layer and a second electrode layer which are electrode layers used for a display element, and the first electrode layer and the second electrode layer are arranged. In this method, a potential difference is generated in the two electrode layers to control the orientation of the spherical particles.

FIG. 10 illustrates active matrix electronic paper as one embodiment of a semiconductor device. The electronic paper in FIG. 10 is an example of a display device using a twisting ball display system.

A black region 4615a and a white region 4615b are provided between the first electrode layer 4030 connected to the transistor 4010 and the second electrode layer 4031 provided for the second substrate 4006, and the periphery is filled with a liquid. A spherical particle 4613 including a cavity 4612 is provided, and the periphery of the spherical particle 4613 is filled with a filler 4614 such as a resin. The second electrode layer 4031 corresponds to a common electrode (counter electrode). The second electrode layer 4031 is electrically connected to the common potential line.

8A to 10B, as the first substrate 4001 and the second substrate 4006, a flexible substrate can be used in addition to a glass substrate, for example, a light-transmitting plastic substrate or the like. Can be used. As plastic, FRP (Fibergla
An ss-Reinforced Plastics) plate, a PVF (polyvinyl fluoride) film, a polyester film, or an acrylic resin film can be used.
A sheet having a structure in which an aluminum foil is sandwiched between PVF films or polyester films can also be used.

The insulating layer 4021 can be formed using an inorganic insulating material or an organic insulating material. Note that an organic insulating material having heat resistance such as acrylic resin, polyimide, benzocyclobutene resin, polyamide, or epoxy resin is preferably used as the planarization insulating film. In addition to the organic insulating material, a low dielectric constant material (low-k material), a siloxane resin, PSG (phosphorus glass), BPSG (phosphorus glass), or the like can be used. Note that the insulating layer may be formed by stacking a plurality of insulating films formed using these materials.

The formation method of the insulating layer 4021 is not particularly limited, and according to the material, sputtering method, spin coating method, dipping method, spray coating, droplet discharge method (ink jet method, screen printing, offset printing, etc.), roll coating Curtain coating, knife coating, etc. can be used.

The display device performs display by transmitting light from a light source or a display element. Therefore, thin films such as a substrate, an insulating film, and a conductive film provided in the pixel portion where light is transmitted have light-transmitting properties with respect to light in the visible wavelength region.

In the first electrode layer 4030 and the second electrode layer 4031 (also referred to as a pixel electrode layer, a common electrode layer, a counter electrode layer, and the like) that apply voltage to the display element, the direction of light to be extracted and the position where the electrode layer is provided The light transmitting property and the reflecting property may be selected depending on the pattern structure of the electrode layer.

The first electrode layer 4030 and the second electrode layer 4031 include indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, and indium. A light-transmitting conductive material such as tin oxide (ITO), indium zinc oxide, or indium tin oxide to which silicon oxide is added can be used.

The first electrode layer 4030 and the second electrode layer 4031 include tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (N
b) Metals such as tantalum (Ta), chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), silver (Ag) ,
Alternatively, it can be formed by using one or plural kinds thereof from an alloy thereof or a nitride thereof.

Alternatively, the first electrode layer 4030 and the second electrode layer 4031 can be formed using a conductive composition including a conductive high molecule (also referred to as a conductive polymer). As the conductive polymer, a so-called π-electron conjugated conductive polymer can be used. For example, polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, a copolymer of two or more of aniline, pyrrole, and thiophene or a derivative thereof can be given.

In addition, since the transistor is easily broken by static electricity or the like, it is preferable to provide a protective circuit for protecting the driving circuit. The protection circuit is preferably configured using a non-linear element.

As described above, by using the transistor exemplified in Embodiment 1, a highly reliable semiconductor device can be provided. Note that the transistor exemplified in Embodiment 1 has not only the above-described semiconductor device having a display function but also a power device mounted on a power supply circuit, a semiconductor integrated circuit such as an LSI, and an image sensor function for reading information on an object. The present invention can be applied to a semiconductor device having various functions such as a semiconductor device.

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

(Embodiment 3)
The semiconductor device disclosed in this specification can be applied to a variety of electronic devices (including game machines). Examples of the electronic device include a television device (also referred to as a television or a television receiver), a monitor for a computer, a camera such as a digital camera or a digital video camera, a digital photo frame, a mobile phone (a mobile phone or a mobile phone). Large-sized game machines such as portable game machines, portable information terminals, sound reproduction apparatuses, and pachinko machines. Examples of electronic devices each including the liquid crystal display device described in the above embodiment will be described.

FIG. 11A illustrates a laptop personal computer, which includes a main body 3001 and a housing 300.
2, a display unit 3003, a keyboard 3004, and the like. By applying the semiconductor device described in Embodiment 1 or 2, a highly reliable notebook personal computer can be obtained.

FIG. 11B illustrates a personal digital assistant (PDA). A main body 3021 includes a display portion 3023,
An external interface 3025, operation buttons 3024, and the like are provided. There is a stylus 3022 as an accessory for operation. By applying the semiconductor device described in Embodiment 1 or 2, a highly reliable personal digital assistant (PDA) can be obtained.

FIG. 11C illustrates an example of an electronic book. For example, the electronic book 2700 includes a housing 27.
It is composed of two housings 01 and 2703. A housing 2701 and a housing 270
3 is integrated with a shaft portion 2711 and can be opened and closed with the shaft portion 2711 as an axis. With such a configuration, an operation like a paper book can be performed.

A display portion 2705 and a display portion 2707 are incorporated in the housing 2701 and the housing 2703, respectively. The display unit 2705 and the display unit 2707 may be configured to display a continuous screen or may be configured to display different screens. With a configuration in which different screens are displayed, for example, text is displayed on the right display unit (display unit 2705 in FIG. 11C) and an image is displayed on the left display unit (display unit 2707 in FIG. 11C). Can be displayed. By applying the semiconductor device described in Embodiment 1 or 2, a highly reliable e-book reader 2700 can be obtained.

FIG. 11C illustrates an example in which the housing 2701 is provided with an operation portion and the like. For example,
A housing 2701 is provided with a power source 2721, operation keys 2723, a speaker 2725, and the like. Pages can be turned with the operation keys 2723. Note that a keyboard, a pointing device, or the like may be provided on the same surface as the display portion of the housing. In addition, an external connection terminal (such as an earphone terminal or a USB terminal), a recording medium insertion portion, or the like may be provided on the rear surface or side surface of the housing. Further, the e-book reader 2700 may have a structure having a function as an electronic dictionary.

Further, the e-book reader 2700 may have a configuration capable of transmitting and receiving information wirelessly. By radio
It is also possible to purchase desired book data from an electronic book server and download it.

FIG. 11D illustrates a mobile phone, which includes two housings, a housing 2800 and a housing 2801. The housing 2801 is provided with a display panel 2802, a speaker 2803, a microphone 2804, a pointing device 2806, a camera lens 2807, an external connection terminal 2808, and the like. The housing 2800 is provided with a solar cell 2810 for charging the portable information terminal, an external memory slot 2811, and the like. An antenna is incorporated in the housing 2801. By applying the semiconductor device described in Embodiment 1 or 2, a highly reliable mobile phone can be obtained.

The display panel 2802 is provided with a touch panel. A plurality of operation keys 2805 which are displayed as images is illustrated by dashed lines in FIG. Note that a booster circuit for boosting the voltage output from the solar battery cell 2810 to a voltage required for each circuit is also mounted.

In the display panel 2802, the display direction can be appropriately changed depending on a usage pattern. In addition, since the camera lens 2807 is provided on the same surface as the display panel 2802, a videophone can be used. The speaker 2803 and the microphone 2804 are not limited to voice calls,
Recording, playback, etc. are possible. Further, the housing 2800 and the housing 2801 can be slid to be in an overlapped state from the developed state as illustrated in FIG. 11D, so that the size of the mobile phone can be reduced.

The external connection terminal 2808 can be connected to an AC adapter and various types of cables such as a USB cable, and charging and data communication with a personal computer are possible. Further, a recording medium can be inserted into the external memory slot 2811 so that a larger amount of data can be stored and moved.

In addition to the above functions, an infrared communication function, a television reception function, or the like may be provided.

FIG. 11E illustrates a digital video camera including a main body 3051, a display portion (A) 3057,
The eyepiece unit 3053, the operation switch 3054, the display unit (B) 3055, the battery 3056, and the like are included. By applying the semiconductor device described in Embodiment 1 or 2, a highly reliable digital video camera can be obtained.

FIG. 11F illustrates an example of a television set. The television device 9600
A display portion 9603 is incorporated in the housing 9601. Images can be displayed on the display portion 9603. Here, a structure in which the housing 9601 is supported by a stand 9605 is illustrated. By applying the semiconductor device described in Embodiment 1 or 2,
A highly reliable television set 9600 can be obtained.

The television device 9600 can be operated with an operation switch provided in the housing 9601 or a separate remote controller. Further, the remote controller may be provided with a display unit that displays information output from the remote controller.

Note that the television set 9600 is provided with a receiver, a modem, and the like. General TV broadcasts can be received by the receiver, and connected to a wired or wireless communication network via a modem, so that it can be unidirectional (sender to receiver) or bidirectional (sender and receiver). It is also possible to perform information communication between each other or between recipients).

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

310 transistor 320 transistor 330 transistor 340 transistor 350 transistor 360 transistor 370 transistor 380 transistor 390 transistor 400 substrate 401 gate electrode 402 first metal oxide film 403 oxide semiconductor film 404 second metal oxide film 405a source electrode 405b drain electrode 407 Third metal oxide film 408 Capacitance wiring 409 Fourth metal oxide film 410 Conductive layer 411 Metal oxide film 413 Metal oxide film 414 Gate electrode 417 Interlayer film 420 Conductive layer 441 Substrate 442 Substrate 443a Polarizing plate 443b Polarized light Plate 444 Liquid crystal layer 446 Electrode 447 Electrode 450 Light shielding layer 451 Light shielding layer 452 Interlayer film 453 Insulating layer 455 Insulating layer 2700 Electronic book 2701 Housing 2703 Housing 2705 Display portion 707 Display portion 2711 Shaft portion 2721 Power supply 2723 Operation key 2725 Speaker 2800 Case 2801 Case 2802 Display panel 2803 Speaker 2804 Microphone 2805 Operation key 2806 Pointing device 2807 Camera lens 2808 External connection terminal 2810 Solar cell 2811 External memory slot 3001 Main body 3002 Housing 3003 Display unit 3004 Keyboard 3021 Main body 3022 Stylus 3023 Display unit 3024 Operation button 3025 External interface 3051 Main body 3053 Eyepiece 3054 Operation switch 3055 Display unit (B)
3056 Battery 3057 Display part (A)
4001 Substrate 4002 Pixel portion 4003 Signal line driver circuit 4004 Scan line driver circuit 4005 Sealing material 4006 Substrate 4008 Liquid crystal layer 4010 Transistor 4011 Transistor 4013 Liquid crystal element 4015 Connection terminal electrode 4016 Terminal electrode 4018 FPC
4019 Anisotropic conductive film 4021 Insulating layer 4030 Electrode layer 4031 Electrode layer 4032 Insulating film 4510 Partition 4511 Electroluminescent layer 4513 Light emitting element 4514 Filler 4612 Cavity 4613 Spherical particle 4614 Filler 4615a Black region 4615b White region 9600 Television apparatus 9601 Housing Body 9603 Display unit 9605 Stand

Claims (1)

A gate electrode;
A gate insulating film covering the gate electrode and including a stacked structure of a first metal oxide film and a second metal oxide film;
An oxide semiconductor film provided in a region in contact with the second metal oxide film and overlapping with the gate electrode;
A source electrode and a drain electrode electrically connected to the oxide semiconductor film;
A third metal oxide film in contact with the oxide semiconductor film;
A fourth metal oxide film in contact with the third metal oxide film,
Each of the first to fourth metal oxide films includes a group 13 element and oxygen.

Images